1. Field of the Invention
The present invention generally relates to transmission assemblies, and more particularly to a transmission assembly interlock system that prevents the engagement of more than one of shift rail at any given time. Even more specifically, this invention is a three-way, shift rail interlock system that only allows engagement of one of three shift rails, and where one of the shift rails is a creeper rail that is located out of plane with the other shift rails.
2. Description of Related Technology
In the field of transmission assemblies, manually operated, synchronized transmissions include a pair of shift rails that are moved in order to select a gear ratio of the transmission. In a typical construction, an interlock ball and an interlock pin cooperate with a pair of co-planar shift rails to prevent both shift rails from being engaged simultaneously. (For three co-planar shift rails, two interlock balls and an interlock pin would be used.) Large transmissions, such as those available on commercial agricultural tractors, are often provided with a third shift rail known as a creeper rail. The creeper rail is a shift rail that allows for the transmission to be shifted into the lowermost ranges of the transmission. With the known constructions, however, there is no known mechanism by which an interlock is provided to couple the creeper rail with the two other, non-creeper shift rails (hereinafter, for clarity, “range rails”), such that engagement of only one of the range rails or the creeper rail is possible at any given point in time.
U.S. Pat. No. 6,745,878 to Jensen, discloses a shift rail assembly where an interlock is provided between a pair of range rails of the transmission. The range rails each have interlock grooves that interact with a pair of interlock balls. While typically retained in a locked position, an interlock member is capable of engaging both interlock balls and holding them in interlock grooves of each of the range rails to prevent engagement of either or both range rails. The interlock member is also moveable to a release position where it is disengaged from both interlock balls. In this position, the interlock balls will allow one of the range rails to be engaged, but not the other. The interlock member is biased towards the locked position and a linkage couples the interlock member to a clutch pedal. Thus, movement of the clutch pedal to its disengaged position causes the interlock member to move into its release position. Notably, this construction fails to disclose an interlock between the range rails and a creeper rail of the transmission assembly
A problem associated with coupling the range rails to the creeper rail is that the creeper shift rail is typically located in position that is spaced away from the range rails. Complicating this even further is the fact that the creeper rail is typically positioned out of plane from the range rails and that other components of the transmission assembly are typically located between the creeper rail and the range rails. As such, the creeper rail is not accessible via a direct line from the range rails.
In view of the above, it is apparent that there exists a need for a three-way interlock of a transmission assembly; the interlock only allowing for engagement of one of three shift rails, one of the shift rails being a creeper rail, at any given point in time.